From its headwaters at Echo Lake in Hopkinton, Mass., the Charles River glides past yards, saturates wetlands, and slips under highways before emptying into Boston Harbor.

Over the years, this 80-mile odyssey through 23 cities and towns has left what seemed to be a faint imprint on the Charles's tea-colored water. But advances in the ability to detect pollutants are giving scientists a clearer idea of the nature of that imprint  and is also triggering interest in research on whether these pose a threat to the environment and to humans.

The chemicals range from fire retardants and detergent byproducts to prescription drugs, antibiotics, and hormones.

Known as organic-waste contaminants, these compounds pass through sewage-treatment plants virtually untreated. They represent the vanguard of what researchers have dubbed emerging contaminants: chemicals whose presence in US rivers, streams, and lakes has gone undetected for years and whose effects  singly and in combination  on fish, aquatic plants, and humans often are poorly understood.

Last week, the United States Geological Survey (USGS) released its first survey of organic-waste contaminants in US surface waters, and the Charles River has plenty of company. Researchers found organic-waste contaminants in 80 percent of the 139 streams and rivers that were tested in 30 states.

During the course of the survey, which ran from 1999 through 2000, the researchers found 82 compounds out of the 95 they sought.

The researchers acknowledge that the sites were selected because they presented a high likelihood that the contaminants would be found. The survey was as much a test of new sampling technologies as it was an exercise in environmental monitoring. But the target compounds also were selected because several are beginning to appear in scientific journals as potential ecological villains.

According to Herbert Buxton, a USGS scientist who took part in the survey, "Thirty-three compounds are known or suspected to be hormonally active." These chemicals, which include steroids, can affect the growth and development of aquatic life.